feat: add ability to set a custom priority for traefik routing rules

tests/unit/traefik.bats

@@ -81,3 +81,25 @@ teardown() {
   assert_success
   assert_output "python/http.server"
 }
+
+@test "(traefik) traefik:set priority" {
+  run /bin/bash -c "dokku proxy:set $TEST_APP traefik"
+  echo "output: $output"
+  echo "status: $status"
+  assert_success
+
+  run /bin/bash -c "dokku traefik:set $TEST_APP priority 12345"
+  echo "output: $output"
+  echo "status: $status"
+  assert_success
+
+  run deploy_app
+  echo "output: $output"
+  echo "status: $status"
+  assert_success
+
+  run /bin/bash -c "docker inspect $TEST_APP.web.1 --format '{{ index .Config.Labels \"traefik.http.services.$TEST_APP-web-http-12345.loadbalancer.server.port\" }}'"
+  echo "output: $output"
+  echo "status: $status"
+  assert_output "5000"
+}